Field of the Invention
The present invention relates to a charging device for charging a rechargeable battery such as a lithium ion secondary battery, and more particularly to a constant current charging device suitable for quick charging.
Background Art
There are several methods to charge a secondary battery. As a typical charging method, there may be mentioned constant current charging. FIG. 4 is a diagram illustrating a charging current I and a battery voltage VBAT in conventional constant current charging.
At an initial time of charging, the secondary battery is charged with a large current. When the battery voltage VBAT rises and reaches a charging completion voltage VEND (e.g., 4.2V), the charging current is switched to a current which gradually becomes lower. At last, the secondary battery is charged with a prescribed minimum current. When the charging completion voltage VEND is reached, the charging is completed.
[Patent Document 1] Japanese Patent Application Laid-Open No. H8-203563